1. Field of Invention
The present invention relates to blast effects suppression devices used to limit the damage associated with explosions, specifically, to reduction, of impulse and overpressure of compression waves in order to minimize the damages in area being protected.
2. Background of the Invention
Terrorist bombings have always been a problem. In many instances, the bomb or explosive device is placed % close to public buildings, embassies, sensitive (nuclear) installations, often in a parked vehicle. The damage associated with explosion is related to air compression waves (also known as pressure waves or shock waves). The duration of this overpressure may be milliseconds or more, and significant impulse associated with compression wave results in damages to structures (buildings) especially to buildings having large surface areas.
Various means can be used to reduce compression wave effects: solid barriers (including blast mats), foams (foam glass, aqueous foams), plastic bags filled with water, mechanical venting, and chemical agents. Solid barriers and blast mats deflect shock waves or absorb wave energy from shock waves through momentum transfer to supporting structure; therefore, they cannot be used to protect the internal or external surface of the buildings or structures from the impulse associated with the shock wave. In addition, they are not effective in confined spaces.
Foam glass, aqueous foams, and plastic bags filled with water are effective being close to the source of shock wave, if the location of bomb is known. They are not effective in protection of large areas or protection from remote explosions.
Mechanical venting is employed to reduce the overpressure and associated stress in containment structures below the level allowable by design. Being effective in reducing the impulse, it cannot reduce the peak overpressure due to response time problem.
Chemical agents suppress shock waves by extinguishing the combustion process, which generates them. Such agents are effective if used to suppress the explosion at a source.
The examples of explosion and shock wave suppression devices are shown in the following patents granted in Canada:                U.S. Pat. No. 2,284,694 John Donovan et al,        U.S. Pat. No. 2,314,245 John Bureaux et al,        U.S. Pat. No. 2,335,788 Donald Butz et al.        
The U.S. Pat. No. 2,284,694 discloses a method and apparatus for enclosing, controlling and suppressing the explosive destruction of munitions in an explosion chamber. Plastic bags of water are suspended within the chamber over the detonation area and filled with water.
In U.S. Pat. No. 2,314,245, an apparatus for explosive blast suppression, and a method therefor, is disclosed. The apparatus comprises a hemispherical enclosure, positioning means associated with the enclosure, for positioning the explosive device substantially equidistant from any point on the wall. The enclosure is made of composite textile material, comprising one or several layers of a ballistic material.
In U.S. Pat. No. 2,335,788, a blast suppression system is disclosed. The system includes a plurality of command-actuated units located in the immediate vicinity of a bomb. Each of the units has nozzles configured to disperse the suppressant material into the air surrounding the bomb. Preferably, the transmission occurs prior to the explosion of the bomb.
The prior art does not address the issue of absorption and dissipation of peak overpressure and impulse of the compression wave from remote or internal explosions provided the position of explosive charge is unknown. If the impulse is absorbed, it is fully transferred to a supporting structure. Nor the prior art addresses the issue of protection from fuel-air explosives (FAE) and associated compression waves. The FAE shock waves are known as having lower peak pressure, longer duration and higher impulse. It is desirable to provide a device that absorbs the compression wave and reduce the structural and bodily injury caused by the blast over-pressure and associated impulse.